// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:async';
import 'dart:io';

import 'package:built_value/serializer.dart';
import 'package:watcher/watcher.dart';

import 'change_provider.dart';
import 'constants.dart';
import 'daemon_builder.dart';
import 'data/build_target.dart';
import 'src/file_wait.dart';
import 'src/server.dart';

/// The long running daemon process.
///
/// Obtains a file lock to ensure a single instance and writes various status
/// files to be used by clients for connection.
///
/// Also starts a [Server] to listen for build target registration and event
/// notification.
class Daemon {
  final String _workingDirectory;
  final RandomAccessFile? _lock;
  final _doneCompleter = Completer<int>();

  Server? _server;
  StreamSubscription? _sub;

  Daemon(String workingDirectory)
    : _workingDirectory = workingDirectory,
      _lock = _tryGetLock(workingDirectory);

  /// Returns exit code.
  Future<int> get onDone => _doneCompleter.future;

  Future<void> stop({String message = '', int failureType = 0}) =>
      _server!.stop(message: message, failureType: failureType);

  bool get hasLock => _lock != null;

  /// Returns the current version of the running build daemon.
  ///
  /// Null if one isn't running.
  Future<String?> runningVersion() async {
    final versionFile = File(versionFilePath(_workingDirectory));
    if (!await waitForFile(versionFile)) return null;
    return versionFile.readAsStringSync();
  }

  /// Returns the current options of the running build daemon.
  ///
  /// Null if one isn't running.
  Future<Set<String>> currentOptions() async {
    final optionsFile = File(optionsFilePath(_workingDirectory));
    if (!await waitForFile(optionsFile)) return <String>{};
    return optionsFile.readAsLinesSync().toSet();
  }

  Future<void> start(
    Set<String> options,
    DaemonBuilder builder,
    ChangeProvider changeProvider, {
    Serializers? serializersOverride,
    bool Function(BuildTarget, Iterable<WatchEvent>)? shouldBuild,
    Duration timeout = defaultIdleTimeout,
  }) async {
    if (_server != null || _lock == null) return;
    _handleGracefulExit();

    _createVersionFile();
    _createOptionsFile(options);

    final server =
        _server = Server(
          builder,
          timeout,
          changeProvider,
          serializersOverride: serializersOverride,
          shouldBuild: shouldBuild,
        );
    final port = await server.listen();
    _createPortFile(port);

    unawaited(
      server.onDone.then((exitCode) async {
        await _cleanUp(exitCode);
      }),
    );
  }

  Future<void> _cleanUp(int exitCode) async {
    await _server?.stop();
    await _sub?.cancel();
    // We need to close the lock prior to deleting the file.
    _lock?.closeSync();
    final workspace = Directory(daemonWorkspace(_workingDirectory));
    if (workspace.existsSync()) {
      workspace.deleteSync(recursive: true);
    }
    if (!_doneCompleter.isCompleted) _doneCompleter.complete(exitCode);
  }

  void _createPortFile(int port) =>
      File(portFilePath(_workingDirectory)).writeAsStringSync('$port');

  void _createVersionFile() => File(
    versionFilePath(_workingDirectory),
  ).writeAsStringSync(currentVersion);

  void _createOptionsFile(Set<String> options) => File(
    optionsFilePath(_workingDirectory),
  ).writeAsStringSync(options.toList().join('\n'));

  void _handleGracefulExit() {
    var cancelCount = 0;
    _sub = ProcessSignal.sigint.watch().listen((signal) async {
      if (signal == ProcessSignal.sigint) {
        cancelCount++;
        await _server!.stop();
        if (cancelCount > 1) exit(1);
      }
    });
  }
}

RandomAccessFile? _tryGetLock(String workingDirectory) {
  try {
    _createDaemonWorkspace(workingDirectory);
    final lock = File(
      lockFilePath(workingDirectory),
    ).openSync(mode: FileMode.write)..lockSync();
    return lock;
  } on FileSystemException {
    return null;
  }
}

void _createDaemonWorkspace(String workingDirectory) {
  try {
    Directory(daemonWorkspace(workingDirectory)).createSync(recursive: true);
  } catch (e) {
    throw Exception('Unable to create daemon workspace: $e');
  }
}
